Experimental investigation of Fe-Mg distribution between olivine and clinopyroxene: Implications for mixing properties of Fe-Mg in clinopyroxene and garnet-clinopyroxene thermometry Available to Purchase

Experiments conducted in a piston cylinder apparatus at 10.5 kbar, 1000 °C, reveal that the exchange of Fe and Mg between olivine and clinopyroxene is nearly ideal. Fifty-three experimental half-reversals tightly constrain the curve ln K_d vs. Fe/(Fe + Mg). If W_FaF0 = 4500 J/atom, the weighted least-squares regression of the experimental results yields W_HdHi = 3978 ± 423 J/atom and $ΔGrxn0=−7208±174 J/mol$ for the exchange reaction. A Monte Carlo regression yields similar results. Fe-Mg mixing in olivine, in the M1 site of clinopyroxene, in garnet, and in orthopyroxene can be characterized by small symmetrical Margules parameters: 4500, 3978, 1590, and 0 J/atom, respectively.

Attempts to perform similar experiments on Fe-Mg exchange between garnet and clinopyroxene were unsuccessful. However, the olivine-clinopyroxene results can be combined with the results of other studies on Fe-Mg exchange between garnet and olivine to calculate a garnet-clinopyroxene thermometer. The calculated thermometer is highly uncertain but yields temperatures 30–190 °C higher than those suggested by some recently published experimental results. One of the recent studies is likely in error; more experimental studies are needed to resolve the discrepancres.